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Tuesday, July 5, 2011

The good news, and the bad news

After a couple of months sitting doing nothing, my recently acquired Cushcraft MA5B minibeam was finally installed here at the QTH last weekend. Thanks to the diligent assistance of Tony EI4DIB, Don EI6IL and Jim 2I0SBI, it is now up in the air.

The new MA5B in situ at my QTH

That was Saturday, and what a fine day it was. In fact, we had a few gorgeous days here in EI land over the weekend and the EI2KC suntan got developed nicely!

That was the good news. Then came the bad. After testing it was discovered that the antenna wouldn't tune on 20m or 15m, although it was fine on 17m, 12m and 10m. Without using an ATU, the SWR is infinite on 20m and 15m, even on low power. Something is amiss. Now it will have to be taken down again and opened up and examined. And that is another day's work.

I have been able to tune it occasionally on 20m and 15m, but the SWR needle on both my radios (I've tried both, and also an external manual ATU to no avail) has started spiking in the middle of an over. I thought maybe proximity to other dielectrics, namely my Butternut HF-V6, my 30m inverted V and my Antron 99, might be affecting it. So I tested it in a full spin through 360 degrees and the SWR remained infinite throughout. I even went to the trouble of taking my Butternut down (good chance to tighten things up a bit!) and also my inverted V but that didn't change anything.

Sounds like there might be a short or a bad connection somewhere in the MA5B. Not sure if it could be water in the traps or something like that because I don't think the traps are required for 20m, whatever about 15m.

I have made a few nice contacts with the beam though, and having a rotatable antenna at the QTH has been a great novelty! My kids think it's great when it spins around! I worked BY1RX/4 on 17m (it's a rotary dipole on 17/12). I also nabbed JW Svalbard on 20m when I could get it to tune. Whatever is wrong it is not very efficient even when it does tune on 20m. Using the Reverse Beacon Network, I put out a CQ on 20m CW using my Butternut vertical and then the MA5B. The Butternut was being received stronger in North America by W3LPL and WU3A, even though the minibeam was pointing in that direction.

Hopefully whatever is wrong can be rectified quickly, easily and cheaply. But as with all beams, once it's up on a mast, it cannot usually be brought to the ground quickly, unless you have a fold-over beam. Or, indeed, if you own your own crane!!

Anyhow I will try to get the "team" back up at the weekend and see if we can't fix whatever is wrong. In the meantime, I do have other antennas that I can use so I'm not completely stuck. And I can spin the rotator for fun!!

3 comments:

Hi Tony.Before you will disassemble antenna check cable first. Try different one , different length. I had similar issue with 17m and 12m. ..... of my delta. 24meters of my old cable didn`t work , 40meters of RG213 new one - didn`t work! 37m of RG8 Mini 8 - works 100% - perfect SWR.I heard you last night trying PY0FO on 18m.Good signal you had in my location.Good Luck!

Very interesting Ark. Well we will have to try that just in case. I can swap out the coax with something else to see if that makes any difference. It's a strange one alright. Hopefully we'll get to the bottom of it quickly.

On 17m and 12m the MA5B is just a rotary dipole. Glad to hear I am getting out alright. But I did not work him :( Maybe tonight? LOL

Good morning, antennas when they are working all is just great...but...when not it can be frustrating. I have had antennas that work just fine one day and the next nothing. I will say one kinda bit of good news is the trouble seems to be more or less consistent. I have found with my antennas in the past if it was intermittent it was very hard to pin point. Good luck with it Anthony and do blog the results.